1. Field of the Invention
The present invention relates in general to ultrasonic medical or dental tools and, in particular, to an improved magnetostrictive transducer for ultrasonic medical or dental tools including an improved laminated structure that incorporates openings to bond the individual laminates.
2. Description of Prior Developments
Magnetostrictive transducers are well known devices for converting electrical energy into vibrational energy at ultrasonic frequencies. These devices are utilized in a variety of ultrasonic medical and dental tool applications including various types of dental scraping and scaling tools as well as surgical tools for fragmenting tissue.
One Example of such an application is disclosed in U.S. Pat. No. 5,382,162 to Sharp. As shown in FIG. 1, Sharp discloses an ultrasonic dental scaler which typically includes a dental scaler insert 2, a housing 10 and dental scaler electronics 16. The scaler insert 2 includes a magnetostrictive transducer 4, an O-ring 6 and a dental tool 8, as shown.
During operation, the scaler insert 2 is placed within the housing 10, wherein the O-ring 6 provides a water tight seal therebetween. Further, the magnetostrictive transducer 4 interacts with a magnetic field created by an energized coil 12 positioned on the housing 10 to vibrate the scaler insert 2. The scaler electronics 16 control the current supplied to the coil 12 so that the scaler insert 2 is vibrated at an ultrasonic frequency. This causes the dental tool 8 to be vibrated which enables it to scale teeth.
Conventional Magnetostrictive transducers of a laminated structure are described in such patents as U.S. Pat. No. 3,076,904 to Kleesattel, U.S. Pat. No. 3,930,173 to Banko and U.S. Pat. No. 4,986,808 to Broadwin et al. As shown in FIG. 2, such a laminated structure 18 typically includes a plurality of laminates 20 which are bonded together in a stacked configuration. The individual laminates 20 are elongated substantially flat members fabricated from magnetostrictive material such as nickel or a nickel alloy which are coated with a layer of oxide. The oxide serves to insulate the adjacent laminates from each other.
As is further evident from FIG. 2, the laminates 20 are bonded together at each end 22,24 by a brazing process. This brazing process produces brazed ends 22,24 having solder that covers all four sides of the stacked laminates 20. These brazed ends 22,24 are intended to keep the laminates 20 bonded together during operation as well as provide electrical contact between the laminates 20.
However, during operation, a problem arises in regard to these brazed ends 22,24. Since the magnetostrictive transducer 18 operates at an ultrasonic frequency, the individual laminates vibrate at this ultrasonic frequency. This vibration after a long period of time can cause metal fatigue in the abraded ends 22,24 which ultimately results in the solder cracking and the individual laminates 20 spreading part. Once the laminates 20 spread apart, the magnetostrictive transducer 18 is no longer functional and must be either replaced or repaired.
Further, conventional magnetostrictive transducers can also be difficult to fabricate. Since a large number of individual laminates are required to be bonded together, a significant amount of time is required to braze each of the ends. Also, the individual laminates are prone to be deformed during fabrication since the individual laminates are usually pushed along an assembly line before being bonded together.
In view of the above, a need therefor exists for a magnetostrictive transducer which is less susceptible to the metal fatigue that causes the laminations to spread apart. A further need exists for a magnetostrictive transducer that is more readily and easily fabricated.